Method and system for topographic measurement by measuring the distance between a rigid reference member and a surface of an eye

ABSTRACT

The invention is a system and method of measuring the shape of a surface. The corneal topographer specifically shown comprises a rigid reference member having a reference surface of a predetermined shape applied to the surface of the eye. The shape of the reference surface is correlated with the measured information to determine the shape of the corneal surface. Several specific designs are shown that use optical, acoustic, acousto-optic or capacitive techniques to determine a distance between the reference surface and the corneal surface over a multiplicity of data points sufficient in number and spacing to represent the local topography of the surface of the eye.

This application claims priority of PCT application PCT/US93/04158,which is a continuation-in-part of U.S. Ser. No. 07/877,651, filed May1, 1992, now U.S. Pat. No. 5,473,392.

BACKGROUND OF THE INVENTION

This invention relates to measuring the shape of surfaces. Whereas otheruses can be envisioned, the invention has with particular applicabilityto measurement of the corneal surface and to facilitating treatments ofthe eye.

Corneal topography measurements are valuable for planning, performing,and evaluating the effects of surgical procedures. Measurements of thecorneal surface are needed for keratorefractive procedures, whichcorrect a refractive power of the eye by changing the curvature of thecorneal surface. In addition, corneal topography can also be used topredict the results of radial keratotomy, evaluate the design ofepikeratophakia for myopia, diagnose the stage of keratoconus, and guidesuture removal following corneal transplantation.

There are several methods to test and characterize the optical power ofthe eye and the cornea in particular. One of the oldest methods is theSnellis diagram test, wherein a patient is asked to read letters or torecognize shapes from a standard distance. This is a subjective methodwhich requires the patient's cooperation.

Since the corneal curvature and its dioptric power account for aboutthree quarters of the refractive power of the eye, it is important,however, to measure the corneal surface with greater accuracy than theSnellis diagram test provides.

One class of methods of measuring the corneal surface is based on thedeflectometry principle, which utilizes reflection of light from thesmooth corneal tear film (i.e., the lower, oily part of the tear film).In this method, a system of rings is optically projected onto thesurface of the eye. A doctor directly observes the symmetry of thereflected rings and judges the condition of the eye. This qualitativetechnique is quite reliable; however, it is dependent upon the doctor'sexperience.

In recent years, automatic measurement devices which measure the shinysurface of the cornea using deflectometry have been introduced. Theseare computerized systems which analyze distortion of the images of asystem of rings optically projected towards the eye and detected by acamera detection system. The spatially defined system of rings isprojected onto the smooth eye surface from a precisely positioned sourcegoverned by a computer. The reflected pattern is detected by a cameraand stored in the memory of a computer. Using the well-definedcharacteristics of the incident and detected light, the geometricposition of the source and the detector, and the shapes of the incidentand detected pattern the computer calculates the shape of the reflectingsphere.

Such a computerized topographer can be used as a principal guide in alaser system performing corneal sculpturing surgery, to provide thenecessary pre-operative and post-operative corneal measurements, or toprovide the measurements to guide post-operative manipulation of thecornea for reduction of astigmatism. However, during and after eyesurgery, once the epithelium is removed from the eye surface, the localmicrotopology of the eye surface has changed so that the surface of theeye is only partially a specular reflector, and now partially a diffusereflector. Since a diffuse reflector has no fixed relationship betweenthe incident angle and the reflected angle of the projected light, thedescribed deflectometry-based topographer is no longer useful.Furthermore, since both the corneal topographer using deflectometry anda laser beam delivery system of a laser sculpturing system requirepositioning on the optical axis of the eye, there is difficulty inincorporating both systems into one unit designed for intraoperativeuse. In addition, since the vision of a patient during surgery or afterde-epithelization is significantly impaired, it is difficult to achieveproper eye alignment necessary for deflectometric measurement.

Rasterography or fringe phase shifts are methods of determiningtopography of the cornea which are well suited for diffusive surfaces.The method does not require smooth reflective surfaces and images can beobtained on surfaces with some degree of epithelial irregularity. Themethods use an optical pattern, for example, a grid of vertical andhorizontal bars of light projected onto the corneal surface. Theprojected pattern has very well established characteristics includingshape, regularity, and separation of the points. A detection systemregisters and analyzes the deformation of the detected pattern. Acomputer analyses the deformation data and establishes the topography ofthe measured surface. The detection system can be located in any placesince it detects the light from a diffused reflector which reflectslight in all directions. The advantage of this method is that theprojected image can cover the entire cornea including the central visualaccess, far periphery, and limbus, interpalpebral conjunctiva, and lidmargins. This technique, however, is not useful for smooth, shinysurfaces, such as the epithelium surface.

There are other optical methods such as confocal microscopy, sharedinterferometry, infrared interferometry and multi-color interferometrythat can be used to characterize the eye surface but each has itslimitations and fails to meet fully, for instance, the needs in the caseof laser sculpting of the cornea.

Again, as suggested above, in laser sculpting of the cornea, the devicesbased on deflectometry are well tailored to measure the specular typesurface which is the surface of the eye during the initial stages oflaser sculpting procedures, and devices based on rasterography are wellsuited to measure diffuse type corneal surface which occurs after lasersculpturing of the corneal surface was performed, but presently, thereare no entirely satisfactory devices which can precisely measure bothtypes of surfaces, and particular surface which in part are of one typeand in part another. Neither are there devices which can be convenientlyintegrated into surgical laser systems. Furthermore, some of thepreviously mentioned instruments require a patient's cooperation sincehe or she needs to look in some specific direction.

In general, the discussed topographers are based on the assumption thatthe cornea has a conic surface i.e. a sphere, an ellipse, a parabola, ora hyperbola, but in reality, the living cornea is none of these; it isan aspheric section with great individual variation, and hence most ofthe known techniques are not completely accurate.

SUMMARY OF THE INVENTION

According to one aspect of the invention, in laser sculpting of thecornea, the surgeon is informed of the starting profile of the cornealsurface and the surface changes during and after the procedure by asingle instrument which avoids disadvantages of prior instruments.Advantageous by such a corneal topographer is incorporated into thelaser sculpting device itself.

The invention provides a fully automatic corneal topographer which doesnot rely upon postulation of any corneal surface. Topographers accordingto the invention are suitable for incorporation into a laser sculpturingsystem and can reliably measure both specular and diffuse types ofsurfaces, without requiring significant cooperation of the patientduring the measurement procedure.

In one aspect, the invention is a system for determining informationconcerning the topography of a portion of the exterior surface of theeye. The system includes a rigid reference member having a referencesurface of predetermined shape for lying over the portion of the eye;the reference surface being positionable in close proximity to anddirected toward the exterior surface of the eye. The system furtherincludes means for determining distance data between the referencesurface and the exterior surface of the eye over a multiplicity of datapoints sufficient in number and spacing to represent the localtopography of the surface of the eye, and means for determining thedesired information concerning the topography of the surface of the eyefrom the distance data in reference to the predetermined shape of thereference surface.

Preferred embodiments of this aspect of the invention may include one ormore of the following features:

The reference surface of the rigid reference member is concavely shapedto approximate the surface of the eye to enable the space therebetweento have a thin cross-section over the examined portion of the eye,enabling small differences in topography of the eye surface to bedetected as relatively large percentage changes in the distance betweenthe reference surface and the eye.

The rigid reference member is transparent to selected radiation and themeans for determining the distance data include a detector for detectingthe radiation passing through the rigid reference member.

A conformable substance is associated with the rigid reference member.The substance is capable of assuming the conformation of surfacesagainst which it is engaged and filling the space between the surface ofthe eye and the reference surface. The means for determining thedistance data are adapted to determine thickness data of the conformablesubstance filling the space between the reference surface and theexterior surface of the eye.

The reference member is transparent to selected radiation and the meansfor determining the distance between the reference surface and thesurface of the eye may be a white light interferometry system, a singlecolor interferometry system or a laser radar system, all adapted todetermine the distance data.

The reference member further comprises an array of conductive elementsdisposed on the reference surface. Each element forms a first capacitorelectrode and the corresponding corneal surface forms the othercapacitor electrode. The means for determining the distance is acapacitance measurement system adapted to determine the distance databased on the capacitance of the capacitors.

The means for determining the distance data are acoustic means oropto-acoustical means.

The reference member further includes an array of acoustic transducersdisposed on the reference surface and adapted to generate and detectacoustic waves across the distance. The means for determining thedistance data is an acoustic measurement system adapted to determine thedistance data based on the frequency of the acoustic waves.

The reference member is adapted to form with the surface of the eye anacoustic chamber including an acoustic microphone, and the means fordetermining the distance data is an opto-acoustic measurement systemcomprise a light source emitting a light beam of a wavelength selectedfor absorption by a constituent within the chamber, a modulator adaptedto modulate the light beam at a frequency selected to excite acousticwaves by absorption of the modulated radiation in the chamber. Theacoustic microphone is adapted to detect the acoustic waves across themeasured distance which is determined based on the frequency of theacoustic waves.

According to another important aspect of the invention, a system fordetermining information concerning the topography of a portion of theexterior surface of the eye is provided, the system comprising a rigidreference member having a reference surface of predetermined shape, thereference surface being positionable in close proximity to and directedtoward the exterior surface of the eye, a conformable substance capableof assuming the conformation of surfaces against which it is engaged andadapted to fill the space between the surface of the eye and thereference surface of the reference member to conform to the respectivesurfaces, means for determining thickness data regarding the conformedsubstance filling the space over a multiplicity of data pointssufficient in number and spacing to represent the desired informationconcerning the topography of the surface of the eye, and means fordetermining the desired information concerning the topography of thesurface of the eye from the thickness data in reference to thepredetermined shape of the reference surface.

Preferred embodiments of this aspect of the invention have one or moreof the following features.

The reference surface of the rigid reference member is concavely shapedto approximate the surface of the eye to enable the conformablesubstance to have a thin cross section over the examined portion of theeye, enabling small differences in topography of the eye surface to bedetected as relatively large percentage changes in the thickness of thecross-section. The conformable substance comprises a fluid contained bya pliable barrier film supported on the reference member in a manner toconfine the fluid, the film having a surface exposed to the eye that isdefined by a biologically compatible substance. The reference surface isconcave and substantially spherical with a radius of about 8millimeters. The conformable substance contains a constituent whichfluoresces when illuminated by selected radiation such that theintensity of fluorescent emission from points in the substance aredependent upon the thickness of the conformable substance at the points,the system further comprising the reference member being transparent toradiation; a radiation source positioned and adapted to irradiate theconformable substance, when conformed to the surface of the eye and thereference surface, with radiation passing through the reference member;and a detector for detecting the intensity of fluorescent radiationemitted from a multiplicity of points distributed over the conformablesubstance sufficiently to represent the information concerning thetopography of the surface of the eye, the fluorescent radiationreturning through the reference member, the intensities being dependentupon the thickness of the fluorescent material at the respective pointsand constituting the thickness data; preferably in this case theconformable substance comprises a biologically compatible liquidcarrying a biologically compatible fluorescent constituent, confined bya biologically compatible barrier film exposed to engage the eye.

As an alternative, the conformable substance comprises a constituentwhich substantially absorbs radiation passing through the referencemember and is contained within a pliable barrier having a surfaceexposed to the eye formed by a diffusive reflector that producesdiffused radiation when illuminated; preferably in this case, thereference member is transparent to selected radiation and theconformable substance substantially absorbs the radiation such that theintensity of diffusively reflected radiation from points in the pliablebarrier pressed against the surface of the eye are dependent upon thethickness of the conformable substance at the points, the system furthercomprising a radiation source positioned and adapted to irradiate theconformable substance, when conformed to the surface of the eye and thereference surface, with incoming radiation passing through the referencemember, and a detector for detecting the intensity of diffuselyradiation returning from a multiplicity of points distributed over thepliable barrier sufficient to represent the information concerning thetopography of the surface of the eye, the intensities dependent upon thethickness of the conformable substance at the respective points andconstituting the thickness data.

Any of the systems described above may have one or more of the followingfeatures:

The reference member further comprises optical means (e.g., a lens, aFresnel lens) for substantially directing the returning radiation to thedirection of the incoming radiation.

The detector comprises a camera sensitive to radiation received from thereference member. Means are provided for forming an image of detectedradiation received via the reference member and determining energyintensities at points in the image. A filter is provided for selectingthe wavelength of the radiation detected by the detector. Means areprovided to digitize signals of the intensities to obtain the thicknessdata and computer means for analyzing the data, preferably in which thecomputer means being adapted to fit the digitized thickness data to apolynomial, the polynomial containing a low order terms representingtranslational displacements, offset, and angular tilting of the rigidreference member relative to the eye surface, the polynomial alsocontaining higher-order terms representing information about thetopography of the eye and the computer means adapted to eliminate thezero order and first order terms.

The detector comprises a lens for receiving radiation through thereference member, a camera upon which the lens focusses an image of theradiation, the camera adapted to produce analog intensity signals, and aframe grabber for producing digital signals from the analog signal forcomputer analysis.

The system includes means to digitize the thickness data, means toprovide a thickness data polynomial by fitting the digitized data to apolynomial, means to provide detailed data of the reference surface, andmeans to combine the thickness data polynomial with the referencesurface topography to provide information about the topography of theeye.

According to another aspect of the invention, a system is provided fordetermining information concerning the topography of the surface of anobject, in general, comprising a rigid reference member having areference surface directed toward the object, the reference surfacebeing of predetermined shape and the reference member being transparentto radiation, a conformable substance capable of assuming theconformation of surfaces against which it is engaged, the conformablesubstance comprising a constituent which fluoresces when illuminated byradiation passing through the reference member, such that the intensityof fluorescent emissions from points in the substance are dependent uponthe thickness of the substance at the points, means for pressing therigid reference member relatively against the surface of the object inthe manner that the conformable substance conforms, on one side, to thesurface of the object, and on the other side to the reference surface ofthe reference member, a radiation source for irradiating the conformablesubstance, when conformed to the object and the reference surface withradiation passing through the reference member, a detector for detectingthe intensity of fluorescent radiation emitted from a multiplicity ofpoints in the conformable substance sufficient to represent desiredinformation concerning the topography of the surface of the eye, thedetector receiving radiation from the conformable substance through thereference member, and means for determining the topography of thesurface of the object from the thickness data in reference to thepredetermined shape of the reference surface.

According to another aspect of the invention, a system is provided fordetermining information concerning the topography of the surface of anobject, in general, comprising a rigid reference member having areference surface directed toward the object, the reference surfacebeing of predetermined shape and the reference member being transparentto radiation, a conformable substance capable of assuming theconformation of surfaces against which it is engaged, the conformablesubstance comprising a constituent which substantially absorbsradiation, the constituent being contained within a pliable barrierhaving a surface exposed to the surface of the object, the barrier beingformed by a diffusive reflector, means for pressing the rigid referencemember relatively against the surface of the object in the manner thatthe conformable substance conforms, on one side, to the surface of theobject, and on the other side to the reference surface of the referencemember, a radiation source for irradiating the conformable substance,when conformed to the surface of the object and the reference surfacewith radiation passing through the reference member, a detector fordetecting the intensity of diffuse radiation from a multiplicity ofpoints distributed over the pliable barrier sufficient to representdesired information concerning the topography of the surface of the eye,the detector receiving radiation from the multiplicity of points throughthe reference member, intensities of the detected radiation beingdependent upon the thickness of the conformable substance at therespective points and constituting the thickness data, and means fordetermining the topography of the surface of the object from thethickness data in reference to the predetermined shape of the referencesurface.

Other aspects of the invention are methods performing the functions ofthe systems described above. Other advantages and features of theinvention will be apparent from the following description and from theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a corneal topographer embodying theinvention.

FIG. 2 is a diagrammatic view of a reference eye contact system with aconformable substance.

FIG. 3 is a diagrammatic view of the operation of the cornealtopographer for first two preferred embodiments of the invention.

FIG. 3A is an enlarged section of FIG. 3 diagrammatically showing thefirst preferred embodiment using fluorescent measurements.

FIG. 3B is an enlarged section of FIG. 3 diagrammatically showing thesecond preferred embodiment using absorption measurements.

FIGS. 4A and 4B show a flow diagram describing operation of thetopographers.

FIG. 5 is a diagrammatic cross-sectional view of a reference eye contactsystem without a conformable substance; and FIGS. 5A and 5B showdiagrammatically the reference system of FIG. 5 adapted for practicalapplication onto the eye.

FIGS. 6 and 7 are diagrammatic views of the corneal topographerutilizing the reference system of FIG. 5 and an interferometric system.

FIG. 8 is a diagrammatic view of the corneal topographer utilizing thereference system of FIG. 5 and an optical position sensing system.

FIG. 9 is a diagrammatic cross-sectional view of the reference system ofFIG. 5 further including an optical lens; and FIG. 9A showsdiagrammatically the optical function of this lens.

FIG. 10 is a diagrammatic view of the corneal topographer utilizing thereference system of FIG. 5 adapted for acoustic measurements.

FIG. 11 is a diagrammatic view of the corneal topographer utilizing thereference system of FIG. 5 adapted for acousto-optic measurements.

FIG. 12 is a diagrammatic view of the corneal topographer utilizing thereference system of FIG. 5 adapted to measure capacitively the cornealcurvature; and FIG. 12A schematically shows equivalent electricalelements of the reference system of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a corneal topographer of the first embodimentcomprises a reference eye contact system 1 having a conformablesubstance, a detection system 5, a light source 3, and a computer system7. Referring to FIG. 2, eye contact system 1 comprises a rigid referencemember 2 made of a transparent material. Reference member 2 has a rigidconcavely shaped reference surface 4 of predetermined curvature whichconforms to the gross contour expected of eyes. A pliable fluidimpermeable conforming membrane 6 is attached to reference member 2below surface 4 using a fastener ring 15. Membrane 6 confines adye-containing fluid 8 below reference 4. A fluid reservoir and a smallpump, not shown in FIG. 2, can be connected to conforming membrane 6 tovary the amount of fluid present. Conforming membrane 6, while confiningthe fluid, assumes the shape of a surface it is pressed against.

FIG. 1 shows reference eye contact system 1 pressed against the cornealsurface 12. It is expected that the head of a patient will be in asubstantially horisontal position during the examination. The pliablemembrane 6 and the dye-containing fluid 8 enclosed inside are pressedbetween rigid reference member 2 and corneal surface 12 so that thespace between reference surface 4 and the actual surface of the eye isfilled with the dye-containing fluid. The excess fluid and dye are shownpresent on the sides of rigid reference member 2 within conformingmembrane 6. The shape of reference surface 4 approximates the cornealcurvature, and thus the amount of the dye-containing fluid locatedbetween the two surfaces is very small and of shallow depth. Referencesurface 4 is preferably made of a wettable material in order to alwaysfill the space between the two surfaces when eye contact system 1 isapplied to the corneal surface 12.

Referring to FIG. 1, detection system 5 contains an adjustable iris 16for regulating the optical light exposure to a camera 22. The incominglight from reference member 2 is focused by an imaging lens 20 after itis filtered by a wavelength selective filter 18. The filter 18 functionsto separate the wavelength of the light of interest from the totalincoming light passing through iris 16. The detected signal is processedby a frame grabber and a digitizer 24 connected to camera 22 and isinput to a computer 26. Computer 26 is used to analyze and store thedigitized signal.

The first preferred embodiment utilizing the reference eye contactsystem of FIG. 2 is a topographer using a differential method ofmeasuring topography by detecting fluorescent radiation. The fluorescentmaterial is a fluorescing constituent which is totally mixed with fluid8 and confined within conforming membrane 6. Referring to FIG. 3, lightsource 14 irradiates eye contact system 1, and the incoming radiationpasses through transparent rigid reference member 2. The radiation 17reaches the fluid 8 confined between unknown eye surface 12 and knownreference surface 2. The fluorescing fluid is activated by the incidentlight and emits fluorescent radiation 19. This is diagrammatically shownin FIG. 3A. A portion of the emitted fluorescent radiation passesoutwardly through rigid reference member 2 and is detected by detector22.

As mentioned above, the thickness of the fluorescing fluid filling thespace between the two surfaces is very small and varies locally withslight differences between the surfaces. The local thickness of thisfluid contains information about the corneal surface. The intensity ofthe fluorescent light radiated by the fluorescent dye depends, at anypoint on the thickness of the fluorescent dye contained between the twosurfaces. Referring to FIG. 3, detecting system 5 detects fluorescentradiation focused by imaging lens 20 onto camera 22. Filter 18 permitspassage only of the fluorescent light and blocks other incoming lightentering through iris 16. The detected signal is then digitized bydigitizer 24 and stored in the memory of computer 26. The wholemeasurement process is controlled by the computer 26, which also storesthe known source-detector geometry, the shape of reference surface 4,properties of the incident light 17 and of the emitted light 19.

The second preferred embodiment utilizing the reference eye contactsystem of FIG. 2 is a topographer of similar construction using adifferential method of measuring topography by detecting localizedabsorption of light. The absorbing material is an absorbing constituentwhich is totally mixed with fluid 8. The absorbing fluid is againconfined by pliable conforming membrane 6. In this embodiment, thesection of the conforming membrane exposed to the corneal surface 12comprises a diffusive optical scatterer (for example, Teflon®) and theother sections are made of non-reflecting material. In the measurementprocess, referring to FIG. 3, eye contact system 1 is pressed againstcorneal surface 12. Light source 14 irradiates eye contact system 1. Theincoming light passes through transparent rigid reference member 2, theabsorbing fluid, and that incoming light 17 which is not absorbed by thefluid reaches the diffuser section of the conforming membrane 6. Asshown in FIG. 3b, a fraction of light is diffusely reflected and travelsback through the absorbing fluid, thence through transparent referencemember 2 and is detected by detection system 5. The geometry of source14, the known shape of reference surface 4, eye contact system 1, anddetection system 5 are stored in the memory of computer 26. The lightdetected by detection system 5 passes twice through the thickness ofabsorbing fluid confined between known reference surface 4 and theunknown corneal surface 12. The local attenuation of reflected light 19depends, here again on the local thickness of the absorbing fluid, andthus the local intensity of the detected light possesses the desiredinformation about the thickness of the absorbing fluid of eachrespective point over the surface of the cornea. In addition to itsreference function, the rigid reference member 2 may have an opticalfunction. The outside surface of the reference member may have a smallerradius than is the predetermined curvature of reference surface 4. Thus,the reference member concentrates the fluorescent (or diffuselyscattered) light into a selected direction where detector 22 ispositioned. Alternatively, the reference member may be attached to anoptical fiber that collects the fluorescent (or diffusely scatteredradiation) and transmits the radiation to the detector.

Referring to both preferred embodiments, the system performsdifferential thickness measurements. At any instant of time, camera 22of detection system 5 detects intensity of radiation arriving from apoint which is located between the measured corneal surface and knownreference surface 12. This intensity of the fluorescent or diffusivelyreflected radiation is dependent on the local thickness of the mixtureof fluids compressed between the two surfaces at that point. Thedetection system scans an area of approximately 5 mm² of referencemember 2 and forms a large number of adjacent pixels (surface regions ofthe smallest resolution) containing the intensity information for therelated locations. Digitizer 24 digitizes the detected intensities, andstores the three dimensional sets into the memory of computer 26. Eachpixel has x,y coordinates and a thickness value computed from theintensity of the detected radiation. The x,y resolution of the system ofa preferred embodiment is about 50 μm.

From this data, with suitable compensation for the selected geometry ofthe system, computer 26 creates a model of the detected thickness, andincorporate to the model the curvature of reference surface 4 to createa model of the measured corneal surface. This is preferably performed byfitting the detected data to a two dimensional polynomial and adding theresulting topography to the topography of the rigid reference surface 4.The resulting topography represents the measured corneal surface. Thisdifferential topography measurement can have resolution of a fewmicrometers.

FIGS. 4A and 4B schematically show the operation of the topographer.Referring also to FIG. 1, rigid transparent reference member 2 withconformable membrane 13 containing a fluorescent (or absorbing) fluid ispressed against the corneal surface (104). The light source 3 directslight 17 onto reference member 2. The imaging system 106 focussesreturning signal 19 onto camera 22, or in FIG. 4A, camera or CCD 108. Insteps 108, 110, and 112, the returning light is detected, digitized andsaved frame-by-frame in the memory of computer 26 (112 in FIG. 4A). Thecomputer governs the whole process, receives general and/or patientspecific data (114), tests the detected data (116) and rejectsunreliable data. If the dynamic range of the signal is wrong, thecomputer initiates another measurement under improved lightingconditions (118). The computer performs fitting of the data (120). Thefitted data are manipulated to eliminate errors caused by translationaldisplacement or an angular tilt (122). Then, the topography data (126)are compared to the reference topography data (124) that representreference surface 4 and the corneal topography is determined (128). Thecalculation can also take into account patient specific data, forexample, previous corneal topography measurements. The cornealtopography is then displayed (132).

Another type of the corneal reference system is shown in FIG. 5.Reference member 140, made again of an optically transparent material,does not include the conformable substance held in the pliable barrieras is described for the embodiments of FIGS. 1 through 3. Rigidreference system 140 is applied temporarily onto the surface of the eyelike a "contact lens" for the purpose of taking measurements of thecorneal topography. Reference member 140 may include an applicator 150or may also be attached to an optical fiber bundle 143 as shown in FIGS.5A and 5B, respectively. To examine the corneal topography at differentlocations, the introduced light is coupled sequentially to theindividual fibers. Alternatively, the single optical fiber is applied todifferent locations.

Referring to FIG. 5, reference member 140 contacts the corneal surface12 using a spacer ring 142 located on the periphery of reference member140 and outside of the measured region of the corneal surface. Spacerring 142 is designed to maintain a substantially constant displacement,D, between the corneal surface 12 and a reference surface 144. Thecurvature of reference surface 144 is approximately equal to theexpected eye curvature (i.e., 7.7 mm) plus a displacement value, D. Forpractical purposes, the displacement is less than 5 mm. A compact fluidexchange system (not shown in the figure) may be connected to thereference member to facilitate introduction or removal of fluid from thedisplacement space between the corneal and reference surfaces.

Reference member 140 is used for referencing the measured data toreference surface 144. The various measurement systems are employed tomeasure local displacement D_(xy) that depends on the curvaturevariation of the measured eye from the selected curvature of referencesurface 144. For embodiments wherein reference member 140 can bemass-produced relatively inexpensively (e.g., by injection molding),spacer ring 142 is integrally connected to the reference member. Forembodiments wherein production of reference member 140 is relativelyexpensive, the reference member is reusable and spacer ring 142,detachably connected to the reference member, is a disposable part ofthey eye contact system. In either case, the performance of thereference member may be calibrated against a precise standard. Thecalibration values are stored in the system's processor and are used toadjust the measured data. Reference member 140 is used in combinationwith different optical techniques such as optical coherence-domainreflectometry (see for example, Youngquist et al., Optical Letters Vol.12, p. 158, 1987; Hee et al., Journal of Opt. Soc. Am. B Vol. 9, p. 903,1992), wavelength-multiplexed interferometry (see for example, Williamset al., Optics Letters, Vol. 14, p. 542, 1989), white-lightinterferometry (see for example, Flournoy et al., Applied Optics, Vol.11, p. 1907, 1972; Linet al. in "White light Interferometry", IBM J.Res. Development, p. 269, May 1972) for determination of thedisplacement D_(xy).

Referring to FIG. 6, in another preferred embodiment, a Michelsoninterferometer 150 is used to measure D_(xy) across the area ofinterest. This interferometer is similar to the experimental systemdescribed by Youngquist et al. A laser source 152 emits a spatiallycoherent beam 154 that is partially reflected, partially transmitted bya beam splitter 156. A reflected beam 158 is incident onto outer surface146 of the reference member. (For simplicity, the angle of incidence isshown to be 90°). Beam 158 encounters interfaces 146, 144, and 12 and ispartially transmitted and partially reflected back to beam splitter 156.

Beam 160, transmitted through beam splitter 156 is reflected of avibrating reference mirror 162 driven by a piezoelectric transducer 164.Oscillating reference mirror 162 modulates the second leg (i.e.,pathlength) of the interferometer and is used for a heterodyne detectionscheme that reduces the noise effects. Reflected beams 160 and 158 arerecombined (165) and directed to detector 166. The detected signal isprocessed by an analyzer 170. System 150 detects the fundamentalmodulating frequency that displays a maximum when the optical paths ofbeams 158 are equal to path 160 governed by moving mirror 162, i.e.,interference fringes occur when the a time delay of path 160 is equal toany one of the three time delays associated with beams reflected fromsurfaces 146, 144 or 12. Detector 166 outputs a maximum signal when anytwo optical waves have their phases in quadrature (i.e., constructiveinterference). Analyzer 170 preferably measures the amplitude of thefundamental frequency and plots the amplitude as a function of thevibrating mirror displacement. The resolution of the system (i.e., thepeak width) depends on the spatial coherence of the introduced beam(154). The plot of the amplitude vs. the mirror displacement includesthree dominant peaks coming from surfaces 146, 144 and 12, depending onthe index of refraction of the corneal surface (i.e., the epithelium andthe tear fluid, or stroma, or the Bowmans layer after performing apartial refractive keratotectomy) and the index of refraction of therigid reference member. For the topography measurement, the system isadjusted to measure the distance D_(xy) between the peaks associatedwith reference surface 144 and the corneal surface 12. If surface 146 iscovered with an antireflective coating, there is no reflection of thissurface, and the system measures only the other two peaks. The systemscans over the region of interest to determine D_(xy) for a desirednumber of measured points and then determines the corneal topographyusing the measured set of D_(xy) numbers similarly as described in FIGS.4A and 4B.

In another embodiment a white light source is used in system of FIG. 7that is a modification of the Michelson interferometer. the system usestwo light beams 174 and 175 generated by the same source 172. The whitelight fringes appear only when the optical path difference from surfaces146, 144, and 12 of the first branch of the interferometer and a surface200 of the second branch. For precise interferometric measurements it isuseful to know precisely the angle of incidence, the refractive index ofthe examined material and its wavelength dispersion, the mirrorposition, and the measurement is also affected by the reflectingsurfaces and possible haze above the surfaces. The system of FIG. 7utilizes two independent sets of interferometric branches to measurethickness D_(XY) at a selected location 171. The refractive index of therigid reference member is known. The first incident beams 175 isdirectly directed to reference member 140 and the second beam 174 isdirected to a beam splitter 176 that partially reflects the incidentbeam to create a beam 178 and partially transmits the beam into the 183direction. Incident beam 175 is partially reflected and partiallytransmitted to the epithelium surface 12 and reflected back to a mirror180. Beam 181 is reflected from mirror 180 which has adjustable positionto create desired time delay (i.e., interferences fringes), and thembeam 181 is further reflected by beam splitter 176 to interferometer184. Beams 175 and 182 travel an additional optical path proportional tothe thickness of the rigid reference member and the distance between thereference surface 144 and the corneal surface 12. By moving mirror 180by exactly the same amount to create the same time delay, produces whitelight interference at the detector of interferometer 184. The mirrorposition is again measured to directly determine D_(XY) spacing. The setof D_(XY) data is again accumulated for different locations of referencesurface 144 by scanning the reference surface in a circular motion. TheD_(XY) data is then used to determine the corneal topography asdescribed above.

Alternatively, the interferometer uses optical fibers that facilitatepropagation of the introduced and reflected light. The variation of thelight path may be achieved by slight altering the fiber length, forexample, by tightly wrapping the fibers around an oscillatingpiezoelectric crystal. Alternatively, the interferometer can scan thewavelengths of light to determine position of the mirror.

The present invention envisions the use of numerous other opticaltechniques for measurement of the D_(XY) distances (e.g., High precisionposition sensing using diode laser radar techniques as described byAbbas et al. in Laser-Diode Technology and Applications II, SPIE Vol.1219, p.468, 1990; Ranging technique with coherent optical radiationusing a phase shift method as described by Grattan et al. in Laser-DiodeTechnology and Applications II, SPIE Vol. 1219, p.480, 1990)

Referring to FIG. 8, in another preferred embodiment, a laser radarsystem 185 measures the D_(XY) spacing by detecting reflections fromsurfaces 12 and 144 using a frequency chirped, intensity modulated laserbeam. The system includes a laser 188 driven by a RF chirp source 186, adirectional fiber optic coupler 190, a scanning mirror 192, a lightdetector 194, a mixer 196, and a processor 198. Laser 188 emits afrequency chirped, intensity modulated light beam (189) that is coupledto fiber optic coupler 190 having a 50% coupling ratio. The output(189a) from directional coupler 190 is focused by a lens system onto aset of scanning mirrors 190 and is delivered perpendicularly to aselected location (x,y) of surface 146 of rigid reference member 140.The incoming beam (193) is reflected from surfaces 146, 144, and 12 andtravels back to fiberoptic coupler 190. The coupler output beam 191,which is the sum of at least three delayed, overlaying waveforms of theintroduced beam 189, is detected by detector 194. The RF detector output(195) is mixed together with the original frequency chirped waveform(187a) in mixer 196. Mixing of the introduced chirp (187) and reflectedchirp (195) results is a number of frequencies proportional to thedistances of the reflecting surfaces since the round-trip time delay ismuch shorter than the duration of the chirp. The system uses a chirp ofa bandwidth of few gigahertz and duration of on the order ofmillisecond. The intermediate frequency from mixer 196 is Fouriertransformed by processor 198 to determine frequencies of the reflectionsfrom the individual surfaces 146, 144, and 12. In the intermediatefrequency spectrum, the frequency peaks of reference surface 144 and thecorneal surface 12 are resolved to determine the D_(XY) distance. Laser188 is selected to produce a wavelength that has a sufficient reflectionfrom the corneal surface 12, and the power of the emitted light is onthe order of few milliwatt. Scanning mirror system 192 scans beam 193over the entire area of interest to measure the D_(XY) data.

Referring to FIG. 9, another type of the rigid reference member isdesigned to have optical function. Reference member 200 again includes aspacer ring 142 adapted to maintain a substantially constantdisplacement, D, between the corneal surface 12 and reference surface144. A lens 202 is formed by shaping outside surface 203 to have asmaller radius than reference surface 144. The optical power of lens 202is designed to compensate for the eye curvature. The operation ofreference member 200 is illustrated in FIG. 9A. The system's lightsource emits light parallel to axis 206. Parallel rays 204 of anincoming light beam enter reference member 200 and are refracted at anangle corresponding to the lens power. Refracted rays 205 strike anideal corneal surface 12 at a 90° angle and are partially reflected fromthe eye surface. In this case, the reflected rays return exactly on thepath of incoming beam 204 and are detected. However, when the cornealcurvature deviates from the expected "model" curvature, beam 205 isreflected at a different angle than 90°. This beam deviation, directlydependent on the actual corneal curvature.

Reference member 200 may be adapted for use in conjunction with theembodiments of FIGS. 3A and 3B or, alternatively, may be used inconjunction with standard deflectomertic techniques (for example,rasterography, deflectometry or moire deflectometry) to determine thecorneal topography directly. Reference member 200 directs most of thelight reflected from the corneal surface back to their originaldirection; thus the detector can detect more reflected light by scanninga smaller area. The directional properties of the reflected lightdirectly depend on the curvature of the eye. In these measurements, themeasured data are not referenced to reference surface 144 as is done forthe above-described embodiments. Alternatively, a set of Fresnel lensesor holographic lenses may replace lens 202.

Referring to FIG. 10, in another preferred embodiment, the rigidreference system of FIG. 5 is adapted for acoustic measurements.Reference member 210 the reference surface modified to include an arrayof discrete acoustic transducers 212. The reference surface formed byarray 212 is again displaced by distance D from the corneal surface 12using ring 142. The individual transducers (i.e., acoustic sources andmicrophones) of array 212 are of about 200 nm to 600 nm in size and arefabricated photolithographically. Each transducer is contacted by twoleads 214 adapted to excite the transducer at desired acousticfrequencies and to detect the reflected waves in individual regions 213.For simplicity FIG. 10 shows leads 214 contacting the transducer fromthe top in a movable manner; however, in a practical array thetransducers may also be contacted by a set of conducting lines depositedbetween the transducers. These line leads end at the boundaries of array212 where the are contacted in a standard manner. A processor 220governs the operation of ultrasonic system 217. Transmitter 216activates a selected transducer to generate an acoustic wave of adesired frequency in the kHz range. The reflected wave is detected andprocessed by a receiver 218. For each transducer, transmitter 216 scansa range of frequencies to detect a fundamental acoustic frequency(f_(s)) at which a standing wave is created in regions 213. For thisfrequency, processor 220 calculates D_(XY) (D_(XY) =2v/f_(s) ; wherein vis the sound velocity) and correlates measured D_(XY) with the locationof the transducer. Ultrasonic system 217 measures the set of the D_(XY)data and then determines the topography of the eye by accounting for theshape of the reference surface as described above.

Referring to FIG. 11, another embodiment uses opto-acoustical method fordetermination of the local distance (D_(XY)) between the referencesurface 144 and corneal surface 12. Opto-acoustical system 230 uses alaser beam 236 of a high monochromacity tuned to the absorption energyof water molecules 233 present between reference surface 144 and cornealsurface 12 and modulated at a desired frequency. A considerable part ofthe modulated laser beam is absorbed and transformed to thermal energythat excites acoustic waves at the modulation frequency.

The system is governed by a processor 250 that controls a laser source244, acousto-optic modulator 240, a mirror 238 and receiver 234. Laser244 generates a laser beam 242 of a wavelength in the infrared regionselected to be absorbed by vapor molecules 233. Beam 242 is modulated ata desired frequency (f) by acousto-optic modulator 240 and delivered toa selected location (x,y) of reference member 231 using mirror 238.Since the intensity of the laser beam is alternating at an acousticfrequency (f), the absorbed radiation excites acoustic waves of acorresponding frequency between surfaces 144 and 12. The acoustic waveis detected by a microphone (e.g., an optical Golay microphone, aninductive pickup, capacitive pickup, condenser, electrodynamic orelectret microphone). In a preferred embodiment, reference member 231forms a resonant chamber with the microphone located on referencesurface 232 and connected to receiver 234. Acousto-Optic modulator 240scans a range of frequencies to find a resonant frequency (f_(s)) forregion 235 with (x,y) coordinates. From the resonant frequency, thedisplacement value D_(XY) is calculated (D_(XY) =2v/f_(s)). Mirrorsystem 238 is used to scan laser beam 236 over the entire area ofreference member 231. The measured set of D_(XY) data is used todetermine the corneal topography.

Referring to FIG. 12, another embodiment of the present invention uses acapacitance technique for the corneal surface measurement. Theembodiment uses a reference member 260 that includes an array ofconductive elements 262 forming reference surface 144. Reference member260 is applied to corneal surface 12 in a similar manner as thereference members shown in FIGS. 6 through 10. Each element 262 forms acapacitor with a corresponding region of the corneal surface locatedbelow and connected to ground by grounding any body part of the personbeing examined. The local distance, D_(XY), between reference surface144 and corneal surface 12, forming a capacitive element, is measuredcapacitively. An inductance is connected in parallel to each capacitorelement as shown in FIG. 12A.

A capacitance system 270 includes a processor 272, an source 274, and acontacting system 276. Processor 272 selects an individual capacitorwith coordinates (x,y) using contacting system 276 and directs theoperation of source 274. Capacitance C_(XY) of each capacitor element262 is measured by detecting a resonance frequency of a small AC signalapplied to the LC system. The corneal profile is determined by measuringthe local distance, D_(XY), which is proportional to capacitance C_(XY).The measured set of D_(XY) data is again referenced to the shape ofreference surface 144 to determine the corneal topography as describedabove.

The topographer can be a separate system or can be incorporated into asurgical system to provide measurements of the corneal surface duringcorneal surgery. During an eye operation it is useful to establish areference point on the surface of the eye. This point is needed tocompare the shape of the surface before and after surgery. This can bedone by marking a specific point which will be kept for the duration ofthe operation. The marking would be done using a dye and placing a doton the eye surface. This will help the surgeon to know the properorientation of the eye.

During an eye operation the eye are anesthetized, thus the patient willnot feel any discomfort when reference member 2 is pressed to the eyesurface. However, when the corneal topographer is used as a stand-aloneunit, some patients might feel discomfort or pain when the referencemember is applied to the eye surface. In these cases, the eye will beanesthetized before the reference member is applied.

Other embodiments are within the following claims:

I claim:
 1. A system for determining information concerning thetopography of a portion of the exterior surface of the eye, the systemcomprising:a rigid reference member having a reference surface ofpredetermined shape for lying over said portion of the eye; saidreference surface being positionable in close proximity to and directedtoward the exterior surface of the eye, means for determining distancedata between said reference surface and said exterior surface of the eyeover a multiplicity of data points sufficient in number and spacing torepresent the local topography of the surface of the eye, and means fordetermining the desired information concerning the topography of saidsurface of the eye from said distance data in reference to saidpredetermined shape of said reference surface.
 2. The system of claim 1wherein said reference surface of said rigid reference member isconcavely shaped to approximate the surface of the eye to enable thespace therebetween to have a thin cross-section over the examinedportion of the eye, enabling small differences in topography of the eyesurface to be detected as relatively large percentage changes in thedistance between said reference surface and said eye.
 3. The system ofclaim 1 wherein said rigid reference member is transparent to selectedoptical radiation and said means for determining said distance datacomprises an optical detector for detecting said radiation passingthrough said rigid reference member.
 4. The system of claim 3, whereinsaid transparent reference member is associated with light refractingmeans for substantially directing radiation passing through saidtransparent member.
 5. The system of claim 3, wherein said detectorcomprises a camera sensitive to radiation received from said referencemember.
 6. The system of claim 3, including means for forming an imageof detected radiation received via said reference member and fordetermining energy intensities at points in said image.
 7. The system ofclaim 3 further includinga light source system positioned and adapted toirradiate through said reference member the corneal surface of the eye,said optical detector constructed to scan an x,y area of said referencemember to collect the passing through light with an x,y resolution onthe order of about 50 μm, a filter for selecting the wavelength of theradiation detected by said detector a digitizer constructed and arrangedto digitize said collected light of said portion of interest of thecorneal surface and create digitized signal, said means for determiningthe desired topography including a computer arranged to receive saiddigitized signal and determine therefrom distance data between saidreference surface and said portion of the corneal surface of the eyeover a multiplicity of x,y data points sufficient in number and spacingto represent the local topography of the corneal surface of the eyerelative to said reference surface, and said computer further arrangedto determine the desired information concerning the topography of saidportion of the corneal surface of the eye from said distance datacorresponding to said x,y data points in reference to said predeterminedshape of said reference surface.
 8. The system of claim 7 wherein saidreference surface of said rigid reference member is concavely shaped toapproximate said portion of the corneal surface of the eye to enable thespace therebetween to have a thin cross-section over the examinedportion of the eye, enabling small differences in topography of thecorneal surface to be detected as relatively large percentage changes inthe distance between said reference surface and said corneal surface ofthe eye.
 9. The system of claim 8 in which the computer is programmed tofit the digitized data to a polynomial, said polynomial containing loworder terms representing translational displacements, offset, andangular tilting of said rigid reference member relative to said eyesurface, said polynomial also containing higher-order terms representinginformation about the topography of the eye.
 10. The system of claim 3,wherein said detector comprisesa lens for receiving radiation throughsaid reference member, a camera upon which the lens focusses an image ofsaid radiation, said camera adapted to produce analog intensity signals,and a frame grabber for producing digital signals from said analogsignal for computer analysis.
 11. The system of claim 3, furthercomprisingmeans for digitizing said data, means for calculating a datapolynomial by fitting said digitized data to a polynomial, means forproviding detailed reference surface topography information, and meansfor combining said data polynomial with said reference surfacetopography information to provide information about the topography ofthe eye.
 12. The system of claim 1 wherein said means for determiningsaid distance data are optical means.
 13. The system of claim 12 whereinsaid reference member is transparent to selected radiation and saidoptical means is a white light interferometry system adapted todetermine said distance data.
 14. The system of claim 12 wherein saidreference member is transparent to selected radiation and said opticalmeans is a single color interferometry system adapted to determine saiddistance data.
 15. The system of claim 12 wherein said reference memberis transparent to selected radiation and said optical means is a laserradar (ladar) system adapted to determine said distance data.
 16. Thesystem of claim 1 wherein said reference member further comprises anarray of conductive elements disposed on said reference surface, eachsaid element forming a first, capacitor electrode and the correspondingcorneal surface forming the other capacitor electrode, and said meansfor determining said distance is a capacitance measurement systemadapted to determine said distance data based on the capacitance of saidcapacitors.
 17. The system of claim 1 wherein said means for determiningsaid distance data are acoustic means.
 18. The system of claim 1 whereinsaid means for determining said distance data are opto-acoustical means.19. The system of claim 1 wherein said reference member furthercomprises an array of acoustic transducers disposed on said referencesurface and adapted to generate and detect acoustic waves across saiddistance, and said means for determining said distance data is anacoustic measurement system adapted to determine said distance databased on the frequency of said acoustic waves.
 20. The system of claim 1wherein said reference member is adapted to form with said surface ofsaid eye an acoustic chamber including an acoustic microphone, and saidmeans for determining said distance data is an opto-acoustic measurementsystem comprisinga light source emitting a light beam of a wavelengthselected for absorption by a constituent within said chamber, amodulator adapted to modulate said light beam at a frequency selected toexcite acoustic waves by absorption of said modulated radiation in saidchamber, said acoustic microphone adapted to detect said acoustic wavesacross said distance, and means for determining said distance data basedon the frequency of said acoustic waves.
 21. A system for determininginformation concerning the topography of a portion of the exteriorsurface of the eye, the system comprising:a member having a rigidsurface of a predetermined shape for overlying said portion of the eye,said rigid surface of predetermined shapes, said reference surface beingpositionable in close proximity to and directed toward the exteriorsurface of the eye, a light source for introducing radiation to saidexterior surface of the eye while said rigid reference member ispositioned adjacent to said surface of the eye, said radiation passingthrough said rigid mender, a light detector for detecting the radiation,returning through said rigid member, reflected from a multiplicity ofpoints over the area of said eye surface sufficient to represent thetopography of the surface of the eye, light refracting means, associatedwith said rigid member, for substantially directing and returningradiation to the direction of said incoming radiation, and means fordetermining the topography of said surface of the eye from saidintroduced radiation and said detected radiation.
 22. The system ofclaim 21 wherein said means for determining topography comprises adeflectometry-based system.
 23. The system of claim 21 wherein saidmeans for determining topography comprises a rasterography-based system.24. The system of claim 21 wherein said means for determining topographycomprises a Moire deflectometry-based system.
 25. A method fordetermining information concerning the topography of a portion of theexterior surface of the eye comprising the steps of:(a) providing arigid reference member having a reference surface of a predeterminedshape; said reference surface lying over said portion of the eye andbeing directed toward the exterior surface of the eye, (b) holding saidrigid reference member stationary to the surface of the eye in themanner that there is a distance between the examined exterior surface ofthe eye and said reference surface of said reference member, (c)determining distance data over a multiplicity of data points sufficientin number and spacing to represent the local topography of said surfaceof the eye, and (d) determining the desired information concerning thetopography of said surface of the eye from said distance data inreference to said predetermined shape of said reference surface.
 26. Themethod of claim 25 wherein reference member is transparent to selectedradiation and said step of determining said distance data is performedusing an optical technique.
 27. The method of claim 26 wherein saidoptical technique is white light interferometry.
 28. The method of claim26 wherein said optical technique is single color interferometry. 29.The method of claim 26 wherein said optical technique is laser radarranging.
 30. The method of claim 25 wherein said reference memberfurther comprises an array of conductive elements disposed on saidreference surface each forming a first capacitor electrode and thecorresponding corneal surface forming the another capacitor electrodeand said step of determining said distance data is performed using ancapacitance technique adapted to determine said distance data based onthe capacitance of said capacitors.
 31. The method of claim 25 whereinsaid step of determining said distance data is performed using anacoustic technique.
 32. The method of claim 25 wherein said step ofdetermining said distance data is performed using an opto-acousticaltechnique.
 33. The method of claim 25 wherein said reference memberfurther comprises an array of acoustic transducers disposed on saidreference surface said step of determining said distance data comprisesthe steps of:(e) generating acoustic waves of different frequenciesacross said distance for each acoustic transducer, (f) detecting anacoustic wave having a resonance frequency, (g) determining a distancebetween said acoustic transducer and said exterior surface of the eyebased on the resonance frequency of said acoustic wave, and (h)repeating steps (e), (f) and (g) for said individual transducers todetermine said distance data.
 34. The method of claim 25 wherein saidreference member is adapted to form with said surface of the eye anacoustic chamber including an acoustic microphone, and said step ofdetermining said distance data comprises the steps of:(e) generating alight beam of a wavelength selected for absorption by a constituentwithin said chamber at a selected location, (f) modulating said lightbeam at a frequency selected to excite acoustic waves by absorption ofsaid modulated radiation in said chamber, (g) detect said acoustic wavesacross said distance, (h) determining said distance, at said selectedlocation, based on the frequency of said acoustic waves, and (i)repeating steps (e), (f), (g) and (h) at another selected location todetermine said distance data over a multiplicity of data pointssufficient in number and spacing to represent the desired informationconcerning the topography of the surface of the eye.
 35. The method ofclaim 25 wherein reference member is transparent to selected opticalradiation and said steps (c) and (d) include:irradiating through saidreference member the corneal surface of the eye, detecting altered lightsignal that is dependent upon a distance between said corneal surface ofthe eye and said reference surface, said detecting step includingscanning an x,y area of said reference member and collecting saidaltered light signal with an x,y resolution on the order of about 50 μm,digitizing said altered light signal of said portion of interest of thecorneal surface, determining from said digitized signal distance databetween said out-of-contact reference surface and said portion of thecorneal surface of the eye over a multiplicity of x,y data pointssufficient in number and spacing to represent the local topography ofthe surface of the eye relative to said reference surface, anddetermining the desired information concerning the topography of saidportion of the corneal surface of the eye from said distance datacorresponding to said x,y data points in reference to said predeterminedshape of said reference surface.
 36. The method of claim 35 wherein saidreference surface is concave and substantially spherical to approximatethe corneal surface of the eye to attain small distance between saidrigid reference surface and said corneal surface over said portion ofthe eye, enabling small differences in topography of the eye surface tobe detected as relatively large percentage changes in the distance data.37. The method of claim 35 or 36 wherein said step of determining thedesired information concerning the topography of said corneal surfacefurther comprising fitting said distance data to a polynomial, saidpolynomial containing low order terms representing translationaldisplacements, offset, and angular tilting of said rigid referencesurface relative to said corneal surface, said polynomial alsocontaining higher-order terms representing information about thetopography of the cornea.
 38. A method for determining informationconcerning the topography of a portion of the exterior surface of theeye comprising the steps of:(a) providing a rigid member having anoutside surface and a inside surface of predetermined shapes, saidinside surface being directed toward the exterior surface of the eye andoverlying said portion of the eye, (b) holding said rigid memberstationary to the surface of the eye, (c) introducing light, passingthrough said rigid member, to said exterior surface of the eye, (d)detecting radiation, returning through said rigid member, reflected froma multiplicity of points over the area of said eye surface sufficient torepresent the topography of the surface of the eye, (e) determining thedesired information concerning the topography of said exterior surfaceof the eye from said introduced and reflected radiation.
 39. The methodof claim 38 wherein said determining step is performed using adeflectometry-based technique.
 40. The method of claim 38 wherein saiddetermining step is performed using a rasterography-based technique. 41.The method of claim 38 wherein said determining step is performed usinga Moire deflectometry-based technique.